Renal therapy blood cleansing system with isolation feature

ABSTRACT

A renal therapy blood cleansing system is provided. The renal therapy blood cleansing system includes a blood filtering device in fluid communication with a blood circuit, a balance chamber configured to exchange like volumes of fresh and used therapy fluid with the blood filtering device, a first pump configured to pump fresh fluid to the balance chamber, a second pump positioned and arranged to receive used fluid from the blood filtering device, and a control scheme. The control scheme is programmed to isolate the blood filtering device from the second pump and deliver a volume of fresh fluid to the blood filtering device via the balance chamber while the second pump is isolated from the blood filtering device, so as to increase fluid volume within the blood circuit.

PRIORITY

This application claims priority to and the benefit as a continuationapplication of U.S. patent application Ser. No. 12/793,906, entitled,“RENAL THERAPY BLOOD CLEANSING SYSTEM WITH BALANCE CHAMBER AND BOLUS,RINSEBACK OR PRIME VOLUME FEATURE”, filed Jun. 4, 2010, which is adivisional application of U.S. patent application Ser. No. 10/738,446,entitled, “MEDICAL FLUID THERAPY FLOW CONTROL SYSTEMS AND METHODS”,filed Dec. 16, 2003, now U.S. Pat. No. 7,744,553, issued Jun. 29, 2010,the entire contents of each of which are incorporated herein byreference and relied upon.

BACKGROUND OF THE INVENTION

The present invention relates to medical systems and more particularlyto medical fluid treatment therapies.

Due to disease, injury or other causes, a person's renal system canfail. In renal failure of any cause, there are several physiologicalderangements. The balance of water, minerals and the excretion of dailymetabolic load are reduced or no longer possible in renal failure.During renal failure, toxic end products of nitrogen metabolism (e.g.,urea, creatinine, uric acid, and others) can accumulate in blood andtissues.

Kidney failure and reduced kidney function have been treated withdialysis. Dialysis removes waste, toxins and excess water from the bodythat would otherwise have been removed by normal functioning kidneys.Dialysis treatment for replacement of kidney functions is critical tomany people because the treatment is life sustaining. One who has failedkidneys could not continue to live without replacing at least thefiltration functions of the kidneys.

Hemodialysis (“HD”), hemofiltration (“HF”), hemodiafiltration (“HDF”)and peritoneal dialysis (“PD”) are types of dialysis therapies generallyused to treat loss of kidney function. Peritoneal dialysis utilizes asterile dialysis solution, or “dialysate”, which is infused into apatient's peritoneal cavity and into contact with the patient'speritoneal membrane. Waste, toxins and excess water pass from thepatient's bloodstream through the peritoneal membrane and into thedialysate. The transfer of waste, toxins, and excess water from thebloodstream into the dialysate occurs due to diffusion and osmosisduring a dwell period as an osmotic agent in the dialysate creates anosmotic gradient across the membrane. The spent dialysate is laterdrained from the patient's peritoneal cavity to remove the waste, toxinsand excess water from the patient.

Hemodialysis treatment removes waste, toxins and excess water directlyfrom the patient's blood. The patient is connected to a hemodialysismachine and the patient's blood is pumped through the machine. Needlesor catheters are inserted into the patient's veins and arteries tocreate a blood flow path to and from the hemodialysis machine. As bloodpasses through a dialyzer in the hemodialysis machine, the dialyzerremoves the waste, toxins and excess water from the patient's blood andreturns the cleansed blood back to the patient. A large amount ofdialysate, for example about ninety to one hundred twenty liters, isused by most hemodialysis machines to dialyze the blood during a singlehemodialysis therapy. Spent dialysate is discarded. Hemodialysistreatment lasts several hours and is generally performed in a treatmentcenter about three times per week.

Hemofiltration is an effective convection-based blood cleansingtechnique. Blood access can be venovenous or arteriovenous. As bloodflows through the hemofilter, a transmembrane pressure gradient betweenthe blood compartment and the ultrafiltrate compartment causes plasmawater to be filtered across the highly permeable membrane. As the watercrosses the membrane, it convects small and large molecules across themembrane and thus cleanses the blood. A large amount of plasma water iseliminated by filtration. Therefore, in order to keep the body waterbalanced, fluid must be substituted continuously by a balancedelectrolyte solution (replacement or substitution fluid) infusedintravenously. This substitution fluid can be infused either into thearterial blood line leading to the hemofilter (predilution), into thevenous blood line leaving the hemofilter (postdilution) or both. Anothertype of therapy, hemodiafiltration, combines the diffusion andconvective cleansing modes of hemodialysis and hemofiltration.

A patient's hematocrit, which is the percentage of red blood cells inthe blood, is about thirty-two to thirty-six percent by volume, leavingthe amount of fluid in the blood to range from about sixty-four tosixty-eight percent. In a typical HDF and HF therapy, blood flow can beabout 300 ml/min, wherein about 100 ml/min of the fluid is being removedthrough the filter, leaving a relatively smaller percentage of the bloodas fluid to exit the hemofilter and to thereafter receive an amount ofdialysate.

Postdilution is a more efficient blood clearance mode than predilutionHF or HDF. In some instances, postdilution HF or HDF can be fiftypercent more efficient than predilution HF or HDF. With postdilutionclearance, however, blood exits the body and enters the filter beforethe extracorporeal circuit receives therapy fluid or dialysate. Becausethe hemodialyzer or hemofilter can remove a good portion of the liquidfrom the patient's blood, postdilution clearance can hemoconcentrate orclot the blood filter. Predilution clearance, on the other hand, infusesfresh therapy fluid into the extracorporeal circuit before the filterand therefore at least substantially reduces the possibility that bloodwill clot in the hemofilter or hemodialyzer.

With predilution HF or HDF, the dialysate is fed into the extracorporealcircuit prior to the hemofilter. Some of that fluid is then immediatelyremoved by the filter, rendering the therapy less effective thanpostdilution therapy. Blood leaving the filter, however, has the samepercentage liquid, e.g., sixty-four to sixty-eight percent, as the bloodleaving the patient, reducing the chances of clotting or aggregatingblood platelets because the blood has too high a percentage of solids.

It is therefore desirable to provide a hemofiltration and/or ahemodiafiltration system that can perform both predilution orpostdilution clearance modes.

It is also desirable to provide an HF and/or an HDF system that providesa priming function, bolus infusion function and/or a blood rinsebackfunction. System priming occurs at the beginning of therapy to removeair from the line, which would be harmful if delivered to the patient.The prime purges the air with a sterile or substantially sterileelectrolyte solution.

At certain times during HF or HDF therapy it is necessary to deliver abolus or relatively large volume of fluid to the patient. It may happenduring therapy that too much blood is removed from the patient tooquickly. The patient's vascular space contains only five to six litersof blood. Removing too much blood too quickly can possibly lower thepressure in the vascular space. The patient's heart rate will quickenand the vascular system will contract in an attempt to compensate forthe loss in blood pressure, however, such measures may not be enough toprevent the patient from becoming hypotensive. In such a case, providinga bolus or volume of fluid to the patient is one effective procedure forincreasing the blood pressure in the vascular system.

It is further desirable to have an HF or HDF system that can provide ablood rinseback at the end of therapy. At the end of therapy there istypically blood that remains in the extracorporeal circuit. It isdesirable to return as much of that blood as possible to the patient. Todo so, the blood therapy system needs to have the ability to pass avolume of fluid through the blood circuit sufficient to push the bloodremaining therein back to the patient.

Both the bolus feature and the rinseback feature present challenges tothe machine manufacturer. For instance, if the machine uses a fluidbalancing system or match flow equalizer that removes an equal amount offluid from the patient for each amount of fluid delivered to thepatient, that balancing system must be accounted for to enable apositive net fluid volume to be delivered to the patient. Second, sincethe fluid is delivered directly to the extracorporeal circuit, the bolusor rinseback fluid needs to be sterile or of an injectable quality.

Removing ultrafiltrate (“UF”) from the patient is a precise operation inwhich a specific amount of fluid needs to be removed from the patientover the course of therapy. The amount of fluid removed from the patienttherefore needs to be carefully monitored. In that regard, problemsarise if the device or devices controlling the UF rate or volume outputfails, e.g., if a valve fails. In such a case, uncontrolled flow fromthe patient can occur causing an overfiltration of the patient. It istherefore desirable to have an ultrafiltration flow control device thatfails in such a way that fluid flow is blocked and uncontrolled UFremoval does not occur.

Certain HF and HDF machines generate the fluid used during therapy atthe time and place that the therapy takes place. Those machines arereferred to as “on-line” machines because they make and provide thesolution on-line. On-line machines use micro or ultrafilters tosterilize the solution or make it of an injectable quality before thesolution is delivered to the patient's extracorporeal circuit. Thefilters over time accumulate bacteria and endotoxin along the outerfiltering surfaces of the membranes located inside the filters. It istherefore desirable to have a method and apparatus that cleans or atleast reduces the amount of bacteria and endotoxin that accumulate andreside along the membranes of the filters used to create dialysateon-line.

SUMMARY OF THE INVENTION

The present invention provides systems and methods for improving medicalfluid delivery systems, such as hemodialysis (“HD”), hemofiltration(“HF”) and hemodiafiltration (“HDF”) systems. The present inventionincludes a multitude of aspects relating to medical fluid flow. In oneaspect, systems and methods for selectively performing pre- andpostdilution HF and HDF clearance modes are provided. In another aspect,systems and methods for providing priming, bolus and rinseback fluidvolumes during/after HF and HDF therapies are provided. In a furtherprimary aspect, improved systems and methods for removing ultrafiltratefrom the patient are provided. In still a further aspect, the presentinvention provides an improved filtration configuration and method.

In one aspect of the present invention, an HF or HDF system is providedthat performs pre- and/or postdilution clearance modes, e.g.,concurrently or simultaneously. The system efficiently uses flowcomponents to perform both pre- and postdilution clearance modes. Forexample, the system does not require an extra pump or an additional pumpsegment to be located in the substitution fluid line, wherein suchadditional components would have to be integrated into the machine toreact appropriately to alarms and operator settings, etc.

The pre/postdilution feature of the present invention instead uses a “Y”connector located at the output of the system's substitution line. Afirst leg of the “Y” connector extends to the postdilution drip chamber.A first check valve is placed on the first leg to prevent blood frombacking into the first leg or substitution fluid infusion line. Thesecond leg of the “Y” can be used for multiple purposes, such as for aconnection to the predilution drip chamber or the arterial line to primethe extracorporeal circuit. In the present invention, the second leg isused to deliver dialysate, prefilter, to the blood line. A second checkvalve is accordingly placed on the second leg to prevent blood frombacking into the substitution line.

Two substitution line pinch clamps are provided, one for each leg outputof the “Y” connector. In one embodiment, when pre- and postdilution aredesired during the same therapy, the arterial line is primed. When thepatient or nurse is ready to connect the dialysate lines to thedialyzer, the second leg of the “Y” connector is connected fluidly to anarterial drip chamber located upstream from the blood pump. The firstleg of the “Y” connector is connected fluidly to the venous dripchamber. The electrically or pneumatically actuated substitution linepinch clamps placed on each of the first and second legs extending fromthe “Y” connector control the amount of substitution fluid used forpredilution and postdilution infusion.

In one embodiment, the operator sets a total target substitution fluidvolume that the patient is to receive. In addition, the operator inputsa percentage pre-versus postdilution setting, for example, by setting aspecific predilution volume or flowrate or postdilution volume orflowrate or enters a percent predilution versus a percent postdilution.Upon starting therapy, the single substitution pump runs continuously,while the clamps alternate to achieve the desired pre- and postdilutionpercentage. For example, if the total substitution flowrate is 150milliliters/minute (“ml/min”) and a fifty ml/min substitutionpredilution flowrate is desired, the postdilution clamp could be closedwhile the predilution clamp is opened for, e.g., five seconds, followedby the predilution clamp being closed and the postdilution clamp beingopened for ten seconds. The result is a continuously running flow offluid into one of the arterial or venous drip chambers, for example, toperform postdilution therapy a majority of the time for its improvedclearance ability, while performing predilution therapy enough of thetime to prevent blood clotting and hypotension.

The system is provided with suitable alarms and assurances, such as asensor that senses if one or both the clamps is in the wrong position,e.g., both clamps being closed at the same time. In such a case, themachine sends an appropriate alarm and takes an appropriate evasiveaction. There are many alternative technologies to sense clamp position,such as via a microswitch, Reed switch, Hall effect switch, opticalsensing, ultrasonic sensing, pressure transducer and the like.

In another aspect of the present invention, an HF/HDF system is providedthat performs special fluid delivery functions, such as a prime, a bolusfunction and a blood rinseback using fluid components in an efficientarrangement. Those function can be commenced manually or automatically,e.g., upon receipt of a signal from a suitable biosensor. In oneembodiment, a two-way isolate valve is placed in the post dialyzertherapy fluid or dialysate circuit. The isolate valve is electrically orpneumatically controlled by the machine controller to perform one of aplurality of functions at a desired time in therapy.

In one implementation, the isolate valve is used to perform a bolusinfusion, e.g., to stabilize the patient who has low blood pressure oris hypotensive. The bolus amount can be predetermined or entered at thetime it is needed. Upon an operator input or suitable signal from asensor, a bypass valve in the upstream dialysate line is closed orde-energized so that normal flow to the dialyzer is stopped and so thatan ultrafiltrate flowmeter is turned off. The isolate valve locateddownstream of the dialyzer is also closed, so that the dialyzer isisolated between the bypass and isolate valves. Transmembrane pressure(“TMP”) alarm limits, operable during normal therapy, are disabled whilethe dialyzer is isolated. A purge valve located upstream from the bypassvalve is opened, allowing post dialyzer fluid sent previously to drainto be drawn through the purge valve to match the flow of fluid to thepatient that flows through the balancing chambers or flow equalizer. Thevolume of fluid flowing to the patient flows through at least onefilter, out of a substitution port, is pumped via the substitution pumpto the venous drip chamber and through the venous access line to thepatient. After the bolus amount is delivered, the purge valve is closedand the patient's blood pressure is allowed to stabilize. Next, theisolate valve is opened, the TMP limits are reset and normal therapy isresumed.

The above apparatus is also suitable to perform a substitution fluidrinseback at the end of therapy to rinse blood remaining in theextracorporeal circuit back to the patient. Here, the operator beginsthe procedure by pressing a “Rinseback” button and perhaps a “Verify”confirmation input. The rinseback feature, like the bolus volume, can beinitiated automatically. An amount of rinseback solution can be presetor set at the time of the procedure. The valve configuration andoperation described above is repeated using the bypass valve, isolatevalve, TMP alarm limits and purge valve. The substitution pump deliversthe programmed rinseback amount to the patient. Again, previouslydiscarded solution is pulled back through the system to balance thefluid flowing to the patient through the match flow equalizer. Here,instead of delivering the amount to the venous dialyzer, as with thebolus solution, the amount is delivered to the arterial access lineprior to the arterial drip chamber, so that as much of theextracorporeal circuit as possible is rinsed.

To communicate the substitution pump with the arterial access line, theoperator can connect the access line to the second leg of the “Y”connector described above. Or, if the system is used in combination withthe pinch clamps described above, the post-dilution clamp is closed andthe predilution clamp is opened, allowing for automatic operation.

The machine is set to alert the operator when the rinseback is complete.After the fluid pressures have stabilized, the purge valve is closed,the isolate valve and bypass valve are opened, the TMP limits areactivated and treatment is ended per the normal procedure.

In a further aspect of the present invention, the machine uses a ceramicpiston rotating reciprocating pump for ultrafiltration (“UF”) instead ofa more complicated, more accident prone and more expensive diaphragmpump type UF flowmeter assembly. The location of the ceramic pump ispredialyzer, immediately downstream of the purge valves. The rotating,reciprocating piston pump is capable of running at a suitable high rateof speed, such as four to eight liters per hour, for rinse and disinfectmodes. During therapy, the pump runs at a flowrate equivalent to thedesired patient UF rate.

The substitution fluid flow and a volumetric equivalent to the patient'sUF is taken from the flow path pre-dialyzer, that is, fresh solution isremoved from the system. In one embodiment, the ceramic pump operateswith balancing chambers that add and remove an equal volume of fluid toand from the system. Any fluid taken from the system by the ceramicpiston pump and any substitution fluid given to the patient as an HDF oran HF infusion is automatically removed from the patient by thepost-flow balancing chamber. The fresh solution is removed from thedialysate flow path, therefore, downstream from the balancing chambersso as not upset the balance of same.

There are many advantages to using the ceramic pump and associated flowconfiguration. The rotating reciprocating ceramic piston pump does notallow flow directly from the input to the output, in contrast to thebalancing chamber type UF flowmeter. If the balancing chamber type of UFdevice fails, there is an uncontrolled flow during half of the cycle,resulting possibly in an overfiltration of the patient. The piston pumpof the present invention, on the other hand, is not subject to that typeof failure, because its input port does not communicate fluidly with thepump's outlet port. If the pump fails, it fails closed, stopping fluidflow. The piston also prevents purge valve errors from causing a UFerror.

The rotations of the pump are monitored using a Reed Switch, opticalsensor, flowmeter, tachometer or other type of feedback device, so thepump rotations and the corresponding ultrafiltration volume removed canbe checked by an independent mechanism. The pump is placed before thedialyzer, preventing the pump from becoming clogged with organicsubstances removed from the dialyzer. The pump is, however, placeddownstream from at least one membrane filter used to help purify thefresh dialysate. That arrangement provides a continual rinse along thesurface of the membranes of the filters. The rinse removes at least aportion of the build-up of bacteria and endotoxin along the membranesurfaces. As a further advantage, the arrangement also removes air fromthe membrane filters during treatment. The removal of the balancingchamber type UF meter and addition of the rotating, reciprocating pumpmakes the flow path of the dialysis system simpler, while improving thesafety and performance of the equipment. The ceramic piston pump in oneembodiment is used to perform the rinseback and bolus infusion featuresthat have been described previously. The pump in those applicationsoperates in the opposite direction so that flow travels to the patient.

In a further aspect, an improved filter configuration and filtrationmethod are provided. The configuration includes at least two filtersplaced in series between pumps or other hydraulically complicated flowmechanisms. The filter portion of the dialysate flow path is simplifiedto reduce the accumulation of bacteria and endotoxin. Also, a pumplocated upstream of the filters is operated to create a higher flowratethan a pump located downstream from the filters. The flow differentialalso helps to strip accumulated bacteria and endotoxins from membranesurfaces located within the filters as well as tubing connecting thefilters.

Each of the above aspects can be employed alone or in any combinationwith one another.

It is therefore an advantage of the present invention to provide ahemofiltration (“HF”) or hemodiafiltration (“HDF”) system that canperform both pre- and postdilution clearance modes with a singlesubstitution pump.

It is another advantage of the present invention to provide an HF or HDFsystem that performs certain net positive fluid flow functions, such asa prime, a bolus function and a rinseback function.

It is a further advantage of the present invention to provide animproved ultrafiltrate flow metering system.

It is yet another advantage of the present invention to provide an HF orHDF system with safety improvement features.

Moreover, it is an advantage of the present invention to provide an HFor HDF system with a simplified flow regime.

Still further, it is an advantage of the present invention to provide anHF or HDF system with performance improvement features.

Yet an additional advantage of the present invention is to provide a HFor HDF system with an improved filtration system and method.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates systems and methods of the present invention forproviding pre- and/or postdilution HF/HDF clearance modes, a bolusvolume to the patient, a prime to the patient and/or a blood rinsebackvolume to the patient.

FIG. 2 illustrates one embodiment of a therapy fluid delivery manifoldused in the systems and methods shown in FIG. 1.

FIGS. 3 and 4 illustrate systems and methods of the present inventionfor removing ultrafiltrate from the patient and for filtering medicaltherapy fluid.

FIGS. 5 to 7 illustrate one embodiment of an ultrafiltrate pump used inthe systems and methods shown in FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides systems and methods for improving medicalfluid delivery systems, such as hemodialysis (“HD”), hemofiltration(“HF”) and hemodiafiltration (“HDF”) systems. In various embodiments,systems and methods for selectively performing pre- and postdilution HFand HDF clearance modes are provided. In other embodiments, systems andmethods for providing bolus, prime and rinseback fluid volumesduring/after HD, HF and HDF therapies are provided. In furtherembodiments, improved systems and methods for removing ultrafiltratefrom the patient are provided. Still further, the present inventionprovides an improved filtration configuration and method.

Pre/Postdilution HDF and HF

Referring now to the drawings and in particular to FIG. 1, an HF and/orHDF system 10 is illustrated. System 10 in one embodiment is part of amachine that can perform HD, HF or HDF as selected by a doctor or nurse.The machine is typically used in a treatment center and in oneembodiment generates dialysis solution via generation unit 12. Onesuitable dialysate generation unit 12 for system 10 is described in themaintenance manual for Baxter's System 1000® therapy machine. It shouldbe appreciated from the disclosure herein, however, that the presentinvention is not limited to dialysate delivery systems or in-centersystems but instead applies to any suitable medical fluid therapytreatment.

Whether system 10 operates in an HF or HDF mode, system 10 includes adialysate flow path 20 and an extracorporeal or blood circuit 70. Indialysate flow path 20, fluid generated via generation unit 12 is pumpedvia a supply pump 14 through a supply regulator 16, which sets themaximum pressure of the dialysate in the flow path. Dialysate path 20employs a number of flow control devices that ensure that the desiredamount of fluid is delivered to and removed from the patient (describedin commonly owned patent U.S. Pat. No. 5,486,286, the teachings of whichare incorporated herein by reference). In particular, dialysate flowpath 20 includes a flow equalizer or balancing chamber 30 and anultrafiltrate flowmeter 50. Flow equalizer 30 includes a pair of fixedvolume chambers 32 and 34 that each have a flexible membrane within,creating four variable volume cavities C1, C2, C3 and C4. For fixedchamber 32, the volume in variable cavity C1 is inversely proportionalto the volume in variable cavity C2. Likewise, for fixed chamber 34, thevolume in variable cavity C3 is inversely proportional to the volume invariable cavity C4.

The two chamber pairs 32 and 34 are provided so that one fixed volumechamber 32 or 34 pumps fluid to the filter/dialyzer, while at the sametime, a second fixed volume chamber 32 or 34 pumps an equal amount offluid from the filter/dialyzer. Match flow equalizer or balancingchamber 30 therefore ensures that any fluid going through equalizer 30is in turn removed from equalizer 30, resulting in a net fluid gain orloss to the patient of zero. Cavities 32 and 34 also alternate so thatin each stroke fluid is pumped to and from the patient, resulting in asteady or non-pulsitile flow profile.

Cavities 32 and 34 operate with inlet valves 36 and outlet valves 38,which are alternated to achieve the above-described flow equalization.In particular, those valves are configured to enable one of the chamberpairs 32 or 34 to receive dialysate flowing through line 18 fromregulator 16 to fill one of the cavities C2 or C4. That filling actioncauses a corresponding one of the cavities C1 or C3 to decrease involume and thereby push used or spent dialysate that filled cavity C1 orC3 in the previous stroke out line 22, through an output pressureequalizer 24, through a blood leak detector 26 and flow restrictor 28 todrain line 40. While that action is happening, a dialysate pressure pump42 is pulling spent dialysate from filter/dialyzer 44 and pushing thatspent dialysate through a pressure regulating recirculation loop 46 tothe other flow chamber pair 32 or 34. Pump 42 pushes fluid into one ofthe variable spent dialysate cavities C1 or C3.

The increasing volume of spent dialysate in the variable chambernecessarily decreases a like volume of fresh dialysate that filledvariable cavity C2 or C4 in the previous stroke, pushing same toward thepatient. Fresh dialysate is pushed out line 48, through output pressureequalizer 24, through a first ultrafilter 52, through a portion offiltration line 88, through a second ultrafilter 54 and through adialysate monitoring manifold 56. Suitable ultrafilter brands arediscussed below. From manifold 56, fresh filtered fluid flows eitherthrough a three-way bypass valve 58, out bypass valve through line 60into filter/dialyzer 44 or out through substitution port 86, through theremainder of filtration line 88 and to blood circuit 70.

As illustrated, a second outlet or bypass line 62 extends from bypassvalve 58 and extends either into post-dialyzer line 64, leading topressure regulating recirculation loop 46, or alternatively extends intorinse line 66 and through rinse valve 68 to drain 40. Bypass line 62,rinse line 66 and rinse valve 68 enable various system components to berinsed or cleaned prior to the beginning of therapy.

Blood circuit 70 includes an arterial access line 72 and a venous accessline 74. Arterial access line 72 includes a Y-connection 76 thatconnects to a dialysate input line described below. Arterial line 72carries blood from patient 78 to an arterial drip chamber 80. Blood istransferred through extracorporeal circuit 70 via a peristaltic bloodpump 82. Pump 82 pumps blood from arterial line 72, through drip chamber80, to the blood inlet of dialyzer 44. The blood is pumped through theinside of membranes contained within the dialyzer, wherein diffusivetransport of toxins and waste products from the blood takes place, andfrom the output of dialyzer 44 into a venous drip chamber 84, throughvenous access line 74, and back to patient 78.

Predialyzer dialysate line 60, dialyzer 44, postdialyzer line 64 and theremainder of dialysate flow path 20 are maintained at a pressure lowerthan that of the blood within circuit 70, resulting in the convectivetransport of waste out of the membranes within dialyzer 44 and atransport of waste and other undesirable substances from the patient'sblood. System 10 is additionally or alternatively capable of performinghemofiltration, in which solution flows along filtration line 88,through substitution port 86, through microfilter/ultrafilter 90,through postfilter line 92, through substitution fluid pump 94 andthrough a pre/postdilution fluid manifold 100, directly to blood circuit70.

Referring additionally to FIG. 2 in combination with FIG. 1,pre/postdilution manifold 100 is illustrated in greater detail. Filter90 in one embodiment is a microfilter. One suitable microfilter is aPall™ Gelman™ single use 0.22 micron filter. In another embodiment,filter 90 is an ultrafilter. One suitable reusable ultrafilter is aMedica™ Diapure™ 28 filter. One suitable single use ultrafilter is aMedica™ 150 u filter. In general, microfilters differ from ultrafiltersin the capability of the different filters in removing small particles.In general, ultrafilters can remove smaller particles than canmicrofilters. For purposes of the present invention, the term“microfilter” includes filters having a membrane pore or membraneopening size of about 1000 to about 105 Angstroms (“Å”), whicheffectively filters particles, such as red blood cells, yeast, fungi,bacteria and some proteins. The term “ultrafilter” as used hereinincludes filters having a membrane pore or membrane opening diameter orlength of about 10 to about 1000 Å, which effectively filters particlessuch as endotoxins (pyrogen), viruses and proteins. In one preferredembodiment, the ultrafilters used in the present invention have a rangeof pore sizes of about 10 to about 40 Å.

Filter 90 operates with ultrafilters 52 and 54 to ensure that a sterileor injectable quality fluid is pumped via substitution pump 94 into thesubstitution fluid manifold 100. Fluid is pumped via pump 94, throughY-connection 102 into either postdilution line 104 or predilution line106. A cap 108 is shown removed from a union 109 located at the end ofpigtail 126 in line 106. Manifold 100 in an alternative embodimentprovides only postdilution line 104 and pigtail 126, wherein remainderof line 106 is removed and the corresponding output from Y-connector 102is capped off via cap 108. The remainder of line 106 can then beselectively added to pigtail 126 by removing cap 108. When predilutionline 106 is fully connected, system 10 can perform either pre- and/orpostdilution HF and HDF as desired.

As seen in FIG. 1, postdilution line 104 extends to the venous dripchamber 84. Predilution line 106 extends in one embodiment to aY-connector or T-connector 76 positioned in a line 73, which is locatedbetween pump 82 and drip chamber 80. In an alternative embodiment, line106 (shown in phantom) extends via a solenoid valve 77 (in phantom) to asecond Y-connector or T-connector 79 located in arterial access line 72,which feeds into post-pump line 73. The alternative embodiment is usedwith a rinseback feature described below. As described in more detailbelow, it is advantageous to connect predilution line 106 to arterialaccess line 72 via connector 79 when system 10 is combined with thebolus, prime and rinseback features described below. It should beappreciated however that the predilution therapy operates equally aswell with line 106 connected to arterial access line 72 via connector 79or to line 73 via connector 76.

A check valve 110 is placed in postdilution line 104, which allows fluidto flow only in the direction from pump 94 to blood circuit 70,preventing blood from backing up through lines 92 and 88 into filters 52and 54 or other parts of dialysate flow path 20. Likewise, a check valve112 is placed in predilution line 106 to prevent blood from backing intodialysate flow path 20 from predilution line 106.

Postdilution line 104 includes a pinch clamp 114. Predilution line 106likewise includes a pinch clamp 116. Suitable pinch clamps for system 10are provided for example by Medica™, Model M03122. Clamps 114 and 116are electrically operated, pneumatically operated or are otherwisecontrolled via a microprocessor of system 10 to be opened and closedselectively as specified by the therapy. Manifold 100 of system 10enables HF or HDF therapy to occur: (i) via postdilution clearance onlyby opening valve 114 and closing valve 116 throughout therapy; (ii) viapredilution clearance only by opening valve 116 and closing valve 114throughout therapy; (iii) via pre- and postdilution clearance modes bysequentially opening valve 114, while valve 116 is closed and thenreversing that state and opening valve 116, while valve 114 is closed;or (iv) via pre- and postdilution clearance modes simultaneously byopening valves 114 and 116 simultaneously.

Although not illustrated, when pre- and postdilution therapy isperformed simultaneously, a variable flow restrictor can be placed ineither one or both pre- and/or postdilution lines 106 and 104,respectively, to partition the percentage flow of dialysate throughlines 104 and 106 as desired (e.g., 80% of flow flows throughpostdilution line 104, while the remaining 20% flows through predilutionline 106). To that end, valves 114 and 116 could instead beneedling-type valves that selectively allow a desired percentage flow topass through lines 104 and 106. Or, such needling valves can be placedin combination with on/off valves 114 and 116, so that there are valvedflow restriction settings and on/off control for both pre- and/orpostdilution clearance modes.

In one embodiment, the operator sets the overall target substitutionvolume into the machine employing system 10. The operator then enters apercentage rate or percentage volume of pre-versus postdilution fluidflow. The single substitution pump 94 runs continuously. The clamps 114and 116 alternate to achieve the desired pre- and postdilution clearancerates. In one example, if the desired percentage breakdown is two-thirdspostdilution and one-third predilution and the total flowrate is 150ml/min, the postdilution clamp could be closed for five seconds, whilethe predilution clamp 116 is open. Afterward, that state is reversed sothat the predilution clamp 116 is closed, while the postdilution clamp114 is open for the next ten seconds. That sequence is repeatedthroughout therapy, or at least the portion of therapy that includesconvective clearance. Alternatively, flow restrictions are placed inlines 104 and 106 and set to produce the desired two-thirds postdilutionof one-third predilution profile, while valves 114 and 116 are openedthroughout the convective clearance portion of the therapy.

The goal of diverting some of the convective flow from postdilution topredilution is to prevent hemoconcentration while providing apredominantly postdilution treatment. To that end, it is desirable notto cycle the valves over too long a period so that such a conditioncould occur. On the other hand, it is also desirable not to cycle thevalves too frequently for wear and maintenance purposes. The desiredcycle time for the valves is therefore chosen to accommodate both ofthose factors.

Bolus and Rinseback Functions

Referring still to FIG. 1, a second primary embodiment of the presentinvention involves the ability of system 10 to perform not only apriming sequence, but to also provide a bolus of fluid to the patient asneeded and to perform blood rinseback at the end of therapy. The bolusfeature and blood rinseback feature are described hereafter in turn.

Bolus Infusion

To provide a bolus or volume of fluid to the patient, for example, whenthe patient has lost too much liquid from the patient's vascular system,the bypass valve 58 is set so that dialysate flow no longer flowsthrough predialyzer line 60 but instead bypasses the filter/dialyzer 44and line 60 and flows alternatively through bypass line 62. Rinse valve68 is closed so that dialysate flowing through line 62 tees intodialysate return line 64, which shunts the fluid through match flowequalizer 30 to drain 40. The bypass valve 58 configuration has theeffect of modifying the dialysate flow path 20 so that dialysate flowbypasses filter/dialyzer 44. As described above, dialysate returningthrough line 64 is cycled through pressure regulating recirculation loop46 via dialysate pump 42. Recirculation loop 46 helps to controlpressure at the inlet of the flow equalizer 30. In particular,recirculation loop 46 operates with input pressure equalizer 118 andsupply regulator 16. Supply pump 14 sets a pressure along line 18. Thatpressure in line 18 moves a diaphragm within input pressure equalizer118 back and forth, which either restricts an orifice that buildspressure in loop 46 or opens the orifice lowering the pressure in theloop, which in turn allows more or less fluid to circulate within loop46.

Besides de-energizing bypass valve 58 so that dialysate flows throughbypass line 62, shutting off flowmeter 50, an isolate valve 120 placedin postdialyzer line 64 is closed. Valves 58 and 120 completely isolatefilter/dialyzer 44 from the remainder of dialysate flow path 20. Tocreate the bolus volume, with filter/dialyzer 44 isolated, purge valve122 is opened to drain. At the same time, a portion of the fluid flowingfrom flow equalizer 30 to bypass valve 58 flows through filtration line88, out of substitution port 86, through filter 90, through postfilterline 92 and is pumped via substitution pump 94 and postdilution line 104(or predilution line 106) through venous drip chamber 84, which purgesany air from the solution, allowing an injectable quality bolus orvolume of fluid to flow into patient 78 via venous access line 74. Sincevalve 122 is connected to an open source of fluid, namely, from fluidpumped via flow equalizer cavities C1 and C3, through blood leakdetector 26, through flow restrictor 28, through line 125 and thoughline 126 (shown with dual directionally pointed arrows), a volumetricequivalent to the fluid pumped to the extracorporeal circuit 70 via pump94 can be infused into the system between the pre and post flowequalizers of equalizer 30. After the fluid flows goes through valve122, the fluid flows through filters 52, 54 and 90 and is monitored forproper conductivity and temperature. Pump 94 will shut down if any ofthose measurements is outside of a correct range.

The control scheme of system 10 is operable to manually or automaticallyinitiate the bolus volume. In one embodiment, the control schemeautomatically commences the bolus feature upon receiving an appropriatesignal from a biosensor, such as a hemoconcentration sensor, a bloodvolume sensor, an electrolyte sensor, an oxygen sensor and anycombination thereof.

It is important to note that the transmembrane pressure (“TMP”) alarmlimits should be disabled or opened during the time that the isolatevalve is closed. The TMP alarms in normal operation ensure that there isa positive pressure differential from the blood circuit 70 to thedialysate flow path 20 through dialyzer 44, so that the net flow ofliquid is from the blood stream to the dialysate flow path 20. Inaddition, the TMP is monitored to detect pressure changes that mayindicate a problem. When isolate valve 120 is closed, the TMP indialyzer 44 isolated between valve 120 and bypass valve 58 may tend toequalize. However, because dialysis is not being performed at thismoment, such equalization is not a concern and thus the alarms are notnecessary.

Flow equalizer 30 requires an equal volume of fluid to flow from line 18to the equalizer as the volume flowing to equalizer 30 fromrecirculation loop 46. It should be appreciated that because there is avolume of fluid being delivered to the patient and no fluid can bepulled from the patient with dialyzer 44 isolated, less fluid wouldreturn to flow equalizer 30 through line 62, compared to the amount offresh fluid delivered to flow equalizer 30 from source 12. Accordingly,a makeup source of fluid is needed. For example, if supply pump 14delivers 300 ml/min to flow equalizer 30 and 100 ml/min is pulledthrough substitution port 86 to the patient, only 200 ml/min will returnthrough bypass line 62, postdialyzer line 64, recirculation loop 46 toflow equalizer 30. The fluid return is deficient by 100 ml/min withrespect to the 300 ml/min global supplied via source 12, and suchdeficiency will cause flow equalizer 30 to operate improperly.

To provide the additional fluid, purge valve 122, which operates withultrafilter 52, is opened during the bolus infusion as discussed above.Purge valves 122 and 124 operate normally with ultrafilters 52 and 54,respectively, to enable the filters to be rinsed prior to therapy.Opening purge valve 122 enables the additional needed fluid, e.g., theadditional 100 ml/min, to be pulled through lines 125 and 126 and intothe dialysate flow path 20. Liquid pulled through drain line 126 haspreviously flowed through dialyzer 44 and been pumped to drain 40 afterpassing through flow equalizer 30. Accordingly, the additional fluidpulled through line 126 needs to be sterilized to be of an injectablequality. The filters 52 and 54 and additional disposable filter 90 infiltration line 88 achieve that requirement. That is, fluid enteringsystem 20 through purge valve 122 flows through ultrafilters 52 and 54,out substitution port 86, through a third ultrafilter or microfilter 90and ultimately to patient 78. Filters 52 and 54 in one embodiment arelarge surface area, reusable filters. Disposable filter 90 can be anultrafilter or a microfilter. Placing three filters in series enablessystem 10 to have triple redundancy during normal operation and for thebolus infusion.

As an extra safety measure, if for some reason the makeup fluid pulledfrom drain line 126 and passing through both filters 52 and 54 does notproduce an injectable quality solution, dialysate monitoring manifold56, which includes a dialysate conductivity probe, temperature sensor, aflow sensor and a dialysate pressure transducer will trip an alarm uponwhich substitution pump 94 is shut down. In the event that an alarm istripped and substitution pump 94 is shut down, the configuration of theperistaltic pump 94 is such that the rotating head clamps the tubing offat a point along the tubing wrapped around the pump head, effectivelystopping flow of fluid at that point.

To deliver the bolus volume, the substitution pump 94 pumps the volumethrough a check valve, such as check valve 110 of post dilution line104, into venous drip chamber 84. It should be appreciated that pre- andpostdilution manifold 100 is not necessary to practice the bolussolution feature of the present invention. However, the bolus solutionvolume can be implemented via pre- and postdilution manifold 100discussed above. To do so, pinch clamp 114 is opened to allow the bolusvolume to pass through check valve 110, pass by clamp 114 and travel vialine 104 to drip chamber 84 or, pinch clamp 116 is opened to allow thebolus volume to pass through check valve 112, pass by clamp 116 via line106 and travel to drip chamber 80. From drip chamber 80 or 84 the bolusvolume travels via venous access line 74 to patient 78.

The amount of the bolus volume is either predetermined or set by theoperator upon initiating the bolus function, for example, via a touchscreen controller. In one embodiment, the bolus amount is set into themachine employing system 10 via a keypad on the touch screen. The amountof bolus can be controlled, for example, by monitoring the number ofrotations of substitution pump 94 or by pumping until a desired settingis achieved on one of the biosensors described above. After the bolusvolume is delivered to the patient, isolate valve 120 is opened, purgevalve 122 is closed, and bypass valve 58 is energized to allow dialysateto flow through predialyzer line 60, and not to line 62. Opening valves120 and 58 re-establishes fluid communication with dialyzer 44. The TMPlimits are accordingly reset or reopened. Prior to opening isolate valve120, one stroke can be taken of the UF flowmeter 50 to help create apositive transmembrane pressure when isolate valve 120 is opened. Thatprocedure may be helpful in achieving a set UF target for the patient.

Blood Rinseback

The blood rinseback feature of the present invention operates in asimilar manner to the bolus infusion feature described above. The bloodrinseback amount can be set at the time the procedure is started orpreset according to a prescription or therapy protocol. Again, a touchscreen having a keypad can be used to set the rinseback amount. Whilethe rinseback function can be initiated manually in one embodiment, thepresent invention also contemplates automatically starting the rinsebackfunction at the end of treatment. Further, while the blood rinsebackprocedure can be controlled by inputting a set amount of fluid, it isalso possible to control the feature via a blood detector placed nearthe patient end of venous access line 74, which detects when no moreblood is present in blood circuit 70 and stops substitution pump 94accordingly and automatically.

Each of the major steps described above for performing the bolusinfusion procedure is also performed for the blood rinseback procedure.Obviously, the procedures are performed at different times duringtherapy because the different procedures are for different purposes. Thebolus function as described above is initiated manually or automaticallywhen the patient appears to have become or is becoming hypotensive.Blood rinseback is performed at the end of treatment to push any bloodremaining in the system back to patient 78. Nevertheless, bothprocedures involve the use of isolate valve 120 and bypass valve 58 toisolate dialyzer 44 from the remainder of dialysate flow path 20. Also,purge valve 122 is opened to enable an equal amount of fluid deliveredto patient 78 to be drawn via drain line 126, through filters 52, 54 and90 into dialysate flow path 20, so that flow equalizer 30 operatesproperly.

One difference between the bolus function and the blood rinsebackprocedure is the location at which the blood rinseback volume isdelivered to extracorporeal circuit 70. As discussed above, the bolusvolume can be delivered to venous drip chamber 84. The rinseback amountis delivered on the other hand to the end of or to a point of arterialaccess line 72 marked by Y-connector or T-connector 79, which isappropriate to clean blood in arterial line 72 through pump 82, througharterial drip chamber 80, through dialyzer 44, through venous dripchamber 84 and finally through venous access line 74 to patient 78.Connector 79 is connected to predilution line 106 via solenoid valve 77to enable automatic control of the rinseback feature. It is contemplatedtherefore to use the pre- and postdilution manifold 100 in combinationwith the rinseback feature of system 10 and to deliver the rinsebackvolume from substitution pump 94, through Y-connector 102, throughpredilution line 106, including check valve 112 and pinch valve 116,through line 106 and solenoid 77, to the arterial access line 72 atconnector 79.

It should be appreciated, however, that manifold 100 is not necessary todeliver the rinseback volume of the present invention. For instance, thefluid connection can be made manually by the operator or nurse. FIGS. 1and 2 show a cap 108 that connects to a union 109 located at the end ofpigtail 126. It is possible that instead of using the already existingpredilution line 106 when the rinseback volume is needed, cap 108 isremoved from the union 109 of pigtail 126 and a substitution line (notillustrated) is manually coupled to the end of pigtail 126 and to eitherconnector 79 of line 72 after being uncoupled from the patient or toconnector 76 located in line 73, for example, by removing a cap fromconnection 76. In a preferred embodiment, that substitution line wouldinclude at its end a one-way valve or check valve, such as check valve112.

To couple the substitution line manually to connectors 76 or 79, bloodpump 82 is shut down and either a cap is removed from connector 79 orthe arterial access line 72 is disconnected from an arterial needle ofthe catheter that is inserted into patient 78. A clamp is closed at theend of the arterial needle so that no blood is lost from the patient.Connector 76 or 79 is then connected to the substitution line, which isalso connected to the end of pigtail 126. In a further alternativeembodiment, a luer connector with a rotating hub is provided in oneembodiment at the end of arterial access line 72 to couple the linedirectly to the substitution line extending from pigtail 126. After thatconnection is made, the rinseback volume is delivered as describedabove.

The known way to provide a rinseback is to connect a saline bag to thearterial access line 72 after disconnecting such line from the arterialneedle. Thereafter, saline flows from the saline bag through thearterial access line 72 to provide the saline rinseback or flush. Boththe manual and automatically operating embodiments described aboveenable system 10 to eliminate the need for a separate saline orinjectable solution supply to provide the blood rinseback.

Prime

The prime feature of the present invention operates using the apparatusdescribed above in connection with FIG. 1 for the bolus and rinsebackfeatures to prime the extracorporeal circuit 70 prior to therapy. Theprime includes a volume of fluid, such as dialysate, that is deliveredat the beginning of the therapy to remove air from the extracorporealcircuit. The prime feature is used within a system or with a controllerthat is operable to receive an operator input to commence delivery ofthe prime. Alternatively, the system or controller is operable tocommence delivery of the prime automatically at the beginning oftherapy. In one embodiment, the amount or volume of the prime is enteredby an operator when commencing delivery of the prime. The amount orvolume can be predetermined prior to commencement of therapy.Alternatively, the amount or volume is delivered until air is no longersensed in the extracorporeal circuit.

UF Flowmeter

Referring now to FIGS. 3 to 7, another primary embodiment of the presentinvention is illustrated. FIGS. 3 and 4 illustrate systems 150 and 160,respectively, which include many of the same components described abovein connection with FIGS. 1 and 2. Those components are marked with thesame element numbers as used in FIGS. 1 and 2. The description of thoseelements including each of the alternatives discussed above inconnection with FIGS. 1 and 2 apply equally to like element numbers inFIGS. 3 and 4.

One primary difference between the embodiments described in FIGS. 1 and2 compared with the systems 150 and 160 of FIGS. 3 and 4 is that the UFflowmeter 50 is removed in FIGS. 3 and 4. The function of the UFflowmeter so shown in FIGS. 1 and 2 is to remove fluid from the patient78 that has accumulated in the patient's body over the time between thepatient's last therapy and the current therapy. One of the problems thatoccurs with kidney failure is that the patient in many instances losessome or all of the ability to urinate. The fluid that would otherwise beremoved from the patient via urination becomes stored in the patient'sblood and surrounding tissues. Thus, while the dialyzer and the infusionof clean solution into patient 78 operate to clear waste products andother undesirable products from patient 78, UF flowmeter 50 operates toremove an additional amount of fluid from the patient, which isequivalent to the amount of fluid gained by the patient betweentreatments.

UF flowmeter 50 operates in a similar manner to one of the chamber pairs32 and 34 of flow equalizer 30. UF flowmeter 50 defines a fixed volumechamber 132 that is separated by a diaphragm into two alternatingvariable volume cavities C5 and C6. Fixed volume chamber 132 is sized ina desired relation to the matched volume chambers 32 and 34. Inletvalves 136 and 138 of UF flowmeter 50 can be cycled with inlet valves 36and outlet valves 38 of flow equalizer 30. In that manner, a knownvolume of fluid is removed with each stroke or valve cycle. The valves136 and 138 alternate so that cavity C6 fills and pushes fluidpreviously drawn into cavity C5 through one of the outlet valves 138,whereafter the valves switch so that cavity C5 fills and pushes thepreviously filled volume in cavity C6 through the other outlet valve138.

UF flowmeter 50 is an effective but relatively complicated device. Also,the failure of one of the valves 136 or 138 can cause an uncontrolledflow during half of a cycle of the diaphragm, resulting in anoverfiltration of the patient.

Another potential problem with system 10 illustrated in FIG. 1 is thatair can become trapped in ultrafilters 52 and 54. It is possible for airto also become trapped in disposable filter 90, however, it is morelikely that air enters reusable filters 52 and 54. Another possibleproblem with system 10 is that dialysate pump 42 is placed directly infront of a UF removal line 134, which leads to UF flowmeter 50. Thatconfiguration can lead to the clogging of UF meter 50. Also, the purgevalves 122 and 124 are closed during normal therapy in system 10, sothat there is no flow across the outside the membranes of those filters(operational flow through filters is from the inlet of the filters tooutside the membranes inside the ultrafilters, through the walls of themembranes, and through the inside of the membranes out the outlet of theultrafilters). The material that is filtered in filters 52 and 54remains inside the filters until a rinse cycle is performed aftertherapy, when purge valves 122 and 124 are opened. That is, bacteria andendotoxin that are filtered by the membranes inside ultrafilters 52 and54 remain inside those filters throughout the duration of therapy.

Another potential problem in system 10 of FIG. 1 is that the only way todetect if one of the purge valves 122 and 124 is not functioningproperly is to detect an increase or decrease in TMP. A TMP error thatis not examined and diagnosed properly by an operator could result in aUF error for the patient.

Referring now to FIGS. 3 and 4, the above-described problems are solvedby removing UF flowmeter 50 and replacing same with a ceramic UF pump140 in dialysate flow path 20. Ultra pure dialysate for online HF andonline HDF treatments is enabled by locating ceramic pump 140 downstreamfrom the single purge valve 122 in system 150 of FIG. 3 and downstreamof dual purge valves 122 and 124 in system 160 of FIG. 4. In both cases,the purge valves are located downstream from the rinse outlet 142 of oneof the ultrafilters 52 or 54. Fluid that reaches pump 140 is thereforefluid that is to be removed along drain line 126. As discussed below,pump 140 is a ceramic rotating, reciprocating piston pump in oneembodiment, which is advantageous because it does not establish fluidcommunication between the inlet and outlet of the pump. That pumpconfiguration enables the pump to fail safe, where uncontrolled fluidflow does not occur.

Locating ceramic pump 140 downstream of purge valves 122 and 124provides additional advantages. That is, besides isolating the inlet andoutlet of the pump and thereby eliminating the potential for UF errordue to component failure, locating pump 140 predialyzer reduces thepossibility of the UF pump becoming clogged or corrupted with organicsubstances. That is, UF removed to drain from pump 140 is clean orsterile solution from generation unit 12. The likelihood of a UFoccurring error due to endotoxin and bacteria building up in the UFremoval device is therefore substantially decreased in systems 150 and160 of the present invention.

Also, because pump 140 pulls fluid from the rinse outlet 142 of filters52 and 54, systems 150 and 160 provide a continual rinse along theoutside of the membranes within those filters. In system 160 of FIG. 4,the purge valves 122 and 124 are cycled, e.g., at fifty percent for eachvalve, so that both filters 52 and 54 are rinsed and cleaned as therapytakes place. The rinse along the outer surface of the membranes offilters 52 and 54 also removes air from the filters continuously orsemi-continuously during treatment. Even though pump 140 removes freshdialysate as UF, dialyzer 44 functions as described above to diffusewaste products from the patient's blood. Waste is also removed throughconvective transport caused by the direct infusion of blood into theextracorporeal circuit 70. That waste is then pumped through balancingchambers 30, via dialysate pump 42, to drain. The UF pumping of freshdialysate via pump 140 does not alter the effectiveness of the therapiesof systems 150 and 160.

As discussed above, one major advantage with using the ceramic rotatingreciprocating piston pump 140 of the present invention is that fluidcommunication does not exist between the inlet and outlet of UF pump140. FIGS. 5 to 7 illustrate one embodiment of UF pump 140, which is arotating and reciprocating piston pump. FIGS. 5 to 7 illustrate therotating reciprocating piston pump 140 in three states, namely, afluid-in state in FIG. 5, a dwell state in FIG. 6 and a fluid-out statein FIG. 7. One suitable rotating reciprocating piston pump is suppliedby Diener Precision Pumps, Embrach, Switzerland.

In FIGS. 5 to 7, valve 140 includes a rotating chamber 142 defining anopening 144 that receives an end of a rotating and reciprocating piston146. The end of the piston 146 includes an arm 148 with a ball bearingtype head 152 that is received slidingly inside a coupling aperture 154,which is in fluid communication with opening 144. As chamber 142 isrotated via a shaft 156 having a substantially vertical axis, head 152is carried by the outer wall of coupler opening 154, which in turnrotates arm 148 and shaft 146. Due to the angle of shaft 146 relative tosubstantially vertical shaft 156, head 152, arm 148 and shaft 146 arealso translated in a direction of the angle of shaft 146 back and forthdepending on the rotational location of coupler opening 154 duringrotation of chamber 142. As illustrated in FIG. 5, during the fluid-instate, piston head 152 is pulled a further distance away from a pumpbody 158 than the vertical distance between piston head 152 and body 158in the fluid-out state of pump 140 in FIG. 7. Piston head 152 isaccordingly at an intermediate relative distance away from body 158 inthe dwell state of pump 140 shown in FIG. 6. It should be appreciated,therefore, that the rotation of drive shaft 156 causes both a rotationalmotion and translational motion of shaft 146 relative to fixed body 158.

Body 158 defines port openings 162 that enable a lubricant such as waterto lubricate the sliding engagement between shaft 146 and the inner boreof body 158. Body 158 also defines inlet and outlet ports 164 and 166,respectively. The lower end of shaft 146 defines a notch 168. Notch 168in the fluid-in state of pump 140 enables fluid to enter via inlet port164 into a pump chamber 170. Importantly, in the fluid-in state, nofluid communication exists between pump chamber 170 and outlet port 166.In the dwell state of pump 140 in FIG. 6, shaft 146 has rotated to aposition wherein notch 168 does not face or communicate with either port164 or 166, so that no fluid communication takes place between pumpchamber 170 and the openings of ports 164 and 166. In the fluid-outstate of pump 140 in FIG. 7, shaft 146 has rotated to a position whereinnotch 168 enables fluid communication to exist between pump chamber 170and outlet port 166. Importantly, in the fluid-out state, no fluidcommunication exists between pump chamber 170 and inlet port 164.

In operation, as the shaft moves from the fluid-out state (FIG. 7) tothe fluid-in state (FIG. 5), the volume in pump chamber 170 increases,creating a vacuum and drawing fluid into chamber 170. In the dwell state(FIG. 6), the volume in pump chamber 170 has decreased from the volumein the fluid-in state (FIG. 5), creating a positive pressure insidechamber 170. As the shaft 146 moves from the dwell state (FIG. 6) to thefluid-out state (FIG. 7), the volume in chamber 170 further decreasesand pushes fluid out of outlet port 166.

Because inlet port 164 never communicates fluidly with outlet port 166,pump 140 even upon a failure or loss of power cannot allow anuncontrolled UF flow, decreasing significantly the inherent errorpotential in comparison to the error inherent in the valves 136 and 138of prior flowmeter 50 and with the flowmeter 50 itself, as well aspotential UF errors that could occur from a failure of one of the purgevalves 122 and 124.

As alluded to above, the amount of ultrafiltrate removed from thepatient is controlled in one embodiment by monitoring the number ofrotations of shaft 146. Rotating, reciprocating piston pump 140 isinherently accurate. If needed, however, a flow measuring device can beplaced in drain line 126 to monitor the output of pump 140.

Pump 140 may also be used with each of the embodiments described abovein connection with FIGS. 1 and 2, including the pre- and postdilutionfeatures, the bolus feature and the rinseback purge. In particular,FIGS. 3 and 4 can employ the manifold 100 discussed above in connectionwith FIG. 1 however same is not shown for the sake of clarity. To infusethe bolus and rinseback volumes, pump 140 rotates in the oppositedirection to pull fluid from line 126 shown with dual directional arrowsin FIGS. 3 and 4 in the same manner as discussed above.

Filtration Configuration

The present invention in FIGS. 1 and 4 shows an improved filtrationconfiguration. To produce a suitable replacement fluid for patient 78,an electrolyte solution such as dialysate is filtered by ultrafiltersand/or microfilters to achieve an injectable quality output. The presentinvention employs three filters in series without an intervening pumpplaced between the filters. The filters each add successive logreduction of bacteria and endotoxin. When a pump is placed between thefilters, the pump becomes a place where bacteria and endotoxinaccumulate during quiescent times, such as when the system is off.Accordingly, the present invention eliminates the need for placing apump between the in-series filters. It should be appreciated howeverthat sensors and other flow components besides pumps are contemplated tobe placed between the in-series filters.

In an attempt to remove as much bacteria and endotoxin as possible, thepresent systems shown in FIGS. 1 and 4 uses three filters in series,namely, filters 52, 54 and 90. Those filters help to ensure the qualityof the solution by providing successive log reductions of bacteria andendotoxin. Filters 52, 54 and 90 can be any combination of single use orreusable ultrafilters, microfilters or other endotoxin/bacteria reducingdevices, such as a clarigen dialguard column. In one embodiment, filters52 and 54 are reusable and the hydraulics path 88 is constructed withoutcomplex hydraulic features, such as a pump, after the first filter inthe system, thereby reducing risk of microbial and biofilm growth afterthe solution is first filtered. In one embodiment, filter 90 is a singleuse microfilter.

For proper log reduction, it is important to lower the potential forbacteria growth and subsequent endotoxin production. To that end, thefiltration configuration of FIGS. 1 and 4 employs no pumps betweenfilters 52, 54 or 90. The flow of medical fluid from filters 52 and 54passes through sterile tubing (and possibly other flow components) tothe inlet of the next filter. Because more complex lumen surfaces offlow components have a greater the chance of forming biofilm, onlytubing is provided in one embodiment between filters 52 and 54 and onlya single dialysate monitoring manifold 56 is placed between filters 54and 90. Limiting the components between filters to only simple tubing(and possibly sensor components) helps to prevent the proliferation ofbacteria on complex surfaces and to ensure the efficacy of thedisinfection.

The purging function during the preparation phase of the medical fluidsystems of the present invention also helps to remove bacteria orendotoxin that may have grown since the machine was last used. With thesimplified flow path between filters 52, 54 and 90, however, very littlegrowth occurs.

Placing pumps before and after the filters 52, 54 and 90 enables theflowrate of fluid pumped, e.g., via dialysate pump 42, through thefilters to be higher than the flowrate pumped, e.g., via infusion pump94, to the patient 78. The systems of FIGS. 1 and 4 can therefore be setso that that the medical fluid flow to patient 78 is only a portion(albeit a potentially large portion) of the total flow out of thefilters, which can be reusable filters. For instance, if the systems areused for hemofiltration and are set to flow 250 ml/min of replacementfluid to patient 78, the flow out of filters 52, 54 and 90 can be 300ml/min. The purpose for that excess flow is to prevent stagnant areas inthe reusable filters at the connections of the filters to filtrationline 88, which helps to ensure that during quiescent times bacteria doesnot proliferate between filters 52 and 54 or after filter 54 in device56 or filtration line 88.

Due to the use of filters in the above-described manner, the quality ofthe replacement fluid can be ensured through the combined log reductionof the filters and because the filters to a large extent only have tofilter contamination from the incoming medical solution. In addition ifone of the filters fails, the resulting log reduction of the remainingfilters in most instances is still sufficient to provide a medical gradesolution. In addition, the smooth clean surfaces in between the filtersare easily and effectively disinfected, preventing growth duringquiescent periods. It should be appreciated that while the filtrationconfiguration described herein is particularly well suited for thesystems of FIGS. 1 and 4, the configuration is expressly not limited tobeing used with the other features and inventions described in thosefigures and indeed is applicable to many different types of injectionfluid flow regimes and configurations.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

The invention is claimed as follows:
 1. A renal therapy blood cleansingsystem comprising: a blood filtering device in fluid communication witha blood circuit; a balance chamber configured to exchange like volumesof fresh and used therapy fluid with the blood filtering device; a firstpump configured to pump fresh fluid to the balance chamber; a secondpump positioned and arranged to receive used fluid from the bloodfiltering device; and a control scheme programmed to (i) isolate theblood filtering device from the second pump and (ii) deliver a volume offresh fluid to the blood filtering device via the balance chamber whilethe second pump is isolated from the blood filtering device so as toincrease fluid volume within the blood circuit.
 2. The renal therapyblood cleansing system of claim 1, wherein the volume of fresh fluid isto compensate for a volume of fluid pumped from the blood filteringdevice being greater than a volume of fluid pumped to the bloodfiltering device.
 3. The renal therapy blood cleansing system of claim1, wherein the volume of fresh fluid is to provide a bolus volume,rinseback volume or prime volume.
 4. The renal therapy blood cleansingsystem of claim 1, which includes at least one valve to isolate theblood filtering device from the second pump.
 5. The renal therapy bloodcleansing system of claim 4, wherein the at least one valve is locatedbetween the blood filtering device and the second pump.
 6. The renaltherapy blood cleansing system of claim 4, wherein the at least onevalve is pneumatically controlled.
 7. The renal therapy blood cleansingsystem of claim 1, wherein the second pump is located between the bloodfiltering device and the balance chamber.
 8. The renal therapy bloodcleansing system of claim 1, which includes a plurality of balancechambers, each balance chamber in communication with the first andsecond pumps.
 9. The renal therapy blood cleansing system of claim 8,wherein the plurality of balance chambers form part of a match flowequalizer.
 10. The renal therapy blood cleansing system of claim 1,which includes an ultrafiltration removal meter configured to remove aknown volume of used therapy fluid from the blood filtering device. 11.The renal therapy blood cleansing system of claim 1, which includes anultrafilter located upstream of the blood filtering device.
 12. A renaltherapy blood cleansing system comprising: a blood circuit including ablood filtering device; first and second balance chambers; a first pumpto pump fresh therapy fluid to the first and second balance chambers; asecond pump positioned and arranged to receive used fluid from the bloodfiltering device and to pump the used fluid to the first and secondbalance chambers; and a control scheme programmed to isolate the secondpump from the blood filtering device and to deliver a volume of freshfluid to the blood filtering device via one of the balance chambers soas to increase fluid volume within the blood circuit.
 13. A medicalfluid method comprising: infusing medical fluid into a blood filteringdevice communicating with a blood circuit using a first pump and abalance chamber that balances the amount of fresh and used treatmentfluid delivered to and removed from the blood filtering device; removingfluid from the blood filtering device using a second pump and thebalance chamber; isolating the blood filtering device from the secondpump; and delivering a volume of fresh medical fluid to the bloodcircuit while the blood filtering device is isolated from the secondpump so as to increase fluid volume within the blood circuit.
 14. Themedical fluid method of claim 13, which includes delivering the volumeof fresh fluid to compensate for a volume of fluid removed from theblood filtering device.
 15. The medical fluid method of claim 13, whichincludes delivering the volume of fresh fluid for priming, rinseback ora patient bolus.
 16. The medical fluid method of claim 13, whichincludes closing at least one valve to isolate the blood filteringdevice from the second pump.
 17. The medical fluid method of claim 18,which includes pneumatically closing the at least one valve.
 18. Themedical fluid method of claim 13, which additionally includes bypassingthe blood filtering device to deliver the volume of fresh medical fluidto the blood circuit.
 19. The medical fluid method of claim 13, whichincludes resuming the infusing and removing steps after the volume offresh medical fluid has been delivered.
 20. The medical fluid method ofclaim 13, which includes enabling the volume of fresh fluid delivered tobe selected proximate to the time of delivery.
 21. The medical fluidmethod of claim 13, which includes enabling the volume of fresh fluiddelivered to be preselected.
 22. The medical fluid method of claim 13,which includes enabling the volume of fresh fluid delivered to becontrolled automatically by delivering the volume until receiving aninput from a sensor.
 23. The medical fluid method of claim 13, whereinthe infusing and removing steps include performing predilution infusion,postdilution infusion or both simultaneously.
 24. The medical fluidmethod of claim 13, which includes delivering the volume automaticallyupon receipt of an input from a biosensor, the biosensor selected fromthe group consisting of a hematocrit sensor, a blood volume sensor, anelectrolytic sensor, an oxygen sensor and any combination thereof. 25.The medical fluid method of claim 13, wherein delivering the volume offresh medical fluid to the blood circuit includes delivering the freshmedical fluid to the blood filter.